Method of and apparatus for pumping liquid oxygen



c. R. ANDERSON 2,480,093

METHOD oF AND APPARATUS FOR PUMPING LIQUID OXYGEN 6 Sheets-Sheet l Aug.23, 1949.

Filed May 27, 194:5

Aug. 23, 1949. c. R. ANDERSON METHOD 0F AND APPARATUS FOR PUMPING LIQUIDOXYGEN Filed May 27, 1943 e sheets-sheet 2 Aug. 23, 1949. c. R. ANDERSONMETHOD OF AND APPARATUS FOR PUMPING LIQUID OXYGEN 6 Sheets-Sheet 3 FiledMay 27, 1943 INVENTOR. AR A. ANofRso/V BY /mfmyzm/w Aug. 23, 1949. c. R.ANDERSON METHOD oF AND APPARATUS FDR PUMPING LIQUID OXYGEN Filed May 27,194s 6 Sheets-Sheet 4 mme INVENTOR.

CARL R. ANDERSQN ATTORNEY Aug. 23, 1949. Q R, ANDERSON 2,480,093

METHOD OF AND APPARATUS FOR PUMPING LIQUID OXYGEN Filed May 2'7, 1943 6Sheets-Sheet 5 CARL l2 ERSU/Q BY y ATTOBNE Y l- 23 1949 c. R. ANDERSON2,480,093

METHOD OF AND APPARATUS FOR PUMPING LIQUID OXYGEN Filed May 27, 1945 6Sheets-Sheet 6 CARL. R. ANDERSON ATTORNEY Patented Aug. 23, 1949 METHODF AND APPARATUS FOR PUMP- lNG LIQUID OXYGEN Cari R. Anderson,

Detroit, Mich., assignor to Air Products Incorporated, Detroit, Mich., acorporation o! Michigan Application May 27, 1943, Serial No. 488,650Claims. (Cl. 62-122) l This invention relates to a method of pumpingliqueed gases and to an apparatus adapted to that use.

An object of the invention is to provide a method and means forwithdrawing a liqueed gas from a vessel in which it is stored or isbeing collected, in such manner as to avoid the POS- sibility of gaslocking the pump.

An object of the invention is to provide a method and means forwithdrawing a stream of liquefied gas of any desired constant quantityfrom a collecting pool in a gas fractionating column.

An object of the invention is to provide a method and means forwithdrawing a stream of gas from a fractionating tower and of reducingthe gas to liquid form for delivery under pressure by means adapted tothe pumping of liquids.

An object of the invention is to provide a method and means for pumpingliqueed oxygen directly from a. pool of commercially pure oxygen in` afractionating tower to cylinders or pipe lines in which gaseous oxygenis transported under high pressure, thereby avoiding the requirement foran oxygen storage tank and a gaseous oxygen compressing system.

An object of the invention is to provide a method and means forwithdrawing oxygen in gaseous form from the pure oxygen vapor space in afractionating tower, for liquefying the gaseous stream and fordelivering the oxygen into pressure cylinders or pipe lines, therebyretaining in the tower any lubricating oil or other combustiblesubstances which may enter the tower with the air stream.

While the invention is applicable to the handling of all liqueed gases(liquids having a boiling point so much below atmospheric temperaturethat heat leakage into insulated apparatus is likely to producedifficulties in pumping), it is found most useful in connection with thepumping of liquid oxygen because of the very low atmospheric-pressureboiling point of this liquid and the fact that the presence, in theapparatus containing the compressed gas at atmospheric temperature, ofany trace of carbonaceous substances is the source of extreme danger.

The invention will therefore be described in connection with themanipulation of oxygen, it being understood that such description isillustrative and not limiting.

In the attached drawings the invention is illustrated schematically, towit:

Fig. 1 illustrates a form in which oxygen in the liquid state is pumpedfrom the pure oxygen pool in a. single fractionating column and thestream is cooled below its boiling point, at the minimum 2 pressureexisting in the pump cylinder, by heat exchange against gaseous productnitrogen from the top of the column.

Fig. 2 illustrates a form in which the same steps are performed inconnection with a double or two-stage fractionating col Figure 3illustrates a modification of Figure 1 wherein product oxygen is takenoff as a. vapor and condensed against the feed air going to the top ofthe column.

Fig. 4 illustrates a modication of Fig. 1

wherein the product nitrogen fromv a single fractionating column passesdirectly to the heat interchanger, and the entering liquid air feedafter being cooledt in the boiling coil immersed in the lower section ofthe column is used to condense the gaseous oxygen stream as well as tosubcool the condensed oxygen stream and cool the pump.

Figs. 5 and 6 illustrate modiications in which all the steps of coolingare applied to the oxygen product of a double fractionating column byinterchange with intermediate fractionation prod= ucts of the column.

The fractionating equipment illustrated is conventional and anypreferred form of either single or double column may be used.

For the purpose of illustration, the single column apparatus of Figs. 1and 3 consists essentially of a, double pass heat interchanger I0,having two banks of tubes II-Ii and Ill-I2, together with afractionating column I3 provided with a plurality of bubbling plates A,and a boiling coil I4 in the base.

The ilows through this system, which also are conventional, are asfollows: Air under pressure, from a source not shown, enters the systemthrough feed pipe I 5, passes through tubes II-IL thence through pipe I6to the boiling coil Il, thence through pipe l1 and expansion valve I8 tothe top of the column, which it enters in a form largely liquid. Flowingdownwardly through the column itis fractionated in the wellknown manner,pure liquid oxygen collecting in a pool I9 in the base of the towerwhile an impure gaseous nitrogen leaves the top of the tower throughpipe 20.

The gaseous nitrogen, after a portion of its refrigerating eiect hasbeen utilized in a manner which will be described, flows through pipe 2|to the shell of interchanger I0. The oxygen is withdrawn from the columnthrough pipe 22, and after various manipulations which will bedescribed, passes through pipe 23 to the tube bank |2|2 of interchangerI0.

In passing through the interchanger in counterow to the entering airstream, the product gaSDuS Oxygen,

oxygen and nitrogen are brought substantially to atmospheric temperatureand pressure in withdrawing heat from the air feed, which is furthercooled and liqueied in supplying heat to the pure oxygen in pool I9.

The double column system illustrated in Figs. 2, and 6 may have the sameinterchanger l0, but the fractlonating column consists of two sections24 and 24', each supplied with bubbling plates A and A'. The uppersection is provided with a condenser 25, the condensate from whichdrains into the lower section of the tower.

The cooled high pressure air from interchanger l0 passes through boilingcoil i4, immersed in a pool 26 of crude (e. g. 35%) oxygen in the baseof the lower section and thence, through pipe l1 and expansion valve i8,into the lower section at a medial height. This section fractionates thefeed in the well-known manner, substantially pure gaseous nitrogenrising into the condenser 25, which is immersed in a pool 21 of pureoxygen collecting in the base of the upper section. As this section ismaintained at a materially lower pressure than the lower section, thecondenser acts as a reboiler for the pure oxygen and returns thenitrogen as a liquid into pool 28, from which a portion overflows to actas reflux in the lower section of the column while the remainder istransferred through pipe 20 and expansion valve 30 to the top oi' theupper section, in which also it acts as reiiux. The crude oxygen istransferred through pipe 3l and expansion valve 32 to a medial point inthe upper section, in which it is fractionated in the well-known mannerto substantially pure oxygen and slightly impure nitrogen.

At this point in either system we have two products-nitrogen andoxygen-each at a temperature which slightly exceeds its atmosphericpressure boiling point. These temperatures are approximately 193centigrade (at 5 pounds gauge) for nitrogen and -1'79 centigrade (at 6pounds gauge) for oxygen.

It is very desirable in many cases to conduct the oxygen productdirectly to the cylinders or pipe lines in which it is transported as acompressed gas, at pressures ranging up to 2500 or more pounds persquare inch. As it is unduly costly (though common practice) to bringthe liquid oxygen to the gaseous form and thereafter compress it, it ishighly desirable to pump it as a liquid and vaporize it prior toentering the pipe line or storage vessel, thus saving an importantamount of power.

A further advantage in pumping the oxygen in liquid phase lies in theavoidance of use of the aqueous lubricants required in compressing theselubricants introducing water vapor which must be removed by chemicaldrying and adsorption to obtain dry oxygen in the transport cylinder orpipe line.

The step of pumping liquid oxygen has Proven in practive to be one ofgreat difilculty. The liquid is, in the nature of the case, at itsboiling point at the existing pressure. From this it iollows that anyreduction in pressure, such as is occasioned by fluid friction in thepump suction, or any increase in temperature due to leakage of heat intothe pump body or to frictional heat transmitted into the liquid, willcause the evolution of gas which locks the suction and puts the pump outof commission. A further cause of vapor lock is back leakage through thedischarge valve, the high pressure leakage liquid partially flashing tothe gaseous state.

A'the pressure existing in Many attempts to solve this problem have beenmade, but so far as I am aware, no method has heretofore been proposedwhich gives satisfactory results in pumping directly from the pool inthe fractionating column, without the interposition of a storage vessel.

I have solved this problem by two steps which are preferably usedtogether but may be used individually. The first is to utilize a smallportion of the cooling effect available in the gaseous product nitrogenfor cooling the steam of liquid oxygen, on its way to the pump, to atemperature below that corresponding to its boiling point at the pumpcylinder during the suction stroke. The second is to utilize anothersmall portion of the refrigerating value of the nitrogen in cooling thepump cylinder.

In the various figures of the instant application, the oxygen pump 33may be any pump capable of handling liquid at high pressure but is hereillustrated as a single acting plunger pump, having a suction valve 34,a discharge valve 35, a cylinder 36, a plunger 31, a rod 3l, a crosshead39. a connecting rod 40, a crank 4I, a worm gear 42, a driving pinion 4land an actuating motor 44.

In the form of the invention shown in Fig. l, the pure oxygen collectingin pool Il flows through pipe 22 to one side of an interchanger 45,thence through pipe 46 and suction valve 34 into the pump cylinder onthe up-stroke of the plunger. On the down stroke the liquid passesthrough discharge valve 35 and pipe 23 to tube bank I2 of interchangeri0, in which the stream is brought to atmospheric temperature and thegaseous condition. and is discharged at any desired pressure throughpipe 4l. If desired, the stream in pipe 23 may be directed to a storagevessel in liquid condition, but more usually it will be passed throughthe interchanger and delivered by pipe 41 to pressure cylinders or otherpressure vessels or to pipe lines in which it is transported underpressure.

The stream of gaseous nitrogen in pipe 20 is passed through the oppositeside of interchanger 45, preferably in counter-flow to the stream ofliquid oxygen, and the liquid is thus cooled to a temperature below itsboiling point at column pressure, preferably from 6 to 8 C. below.

The stream of nitrogen which, because of its relatively great mass, hasbeen only slightly elevated in temperature, iiows through pipe 4l and acoil 49 wrapped around the pump cylinder, in

-which it acts to Withdraw any heat transmitted to the liquid in thepump and tends to maintain the low temperature imparted to the liquid ininterchanger 45.

From this coil the gaseous nitrogen passes through pipe 2l to the shellof interchanger Il, from which it is 'delivered in gaseous form and atsubstantially atmospheric temperature through pipe 50.

In the form shown in Fig. 2 the flows are identical with those abovedescribed with the exception that the liquid oxygen is withdrawn from apool 21 in the upper section of the tower instead of from pool I9 in thebase of the single column.

By the use of this cooling cycle, a. properly designed and insulatedpump may be caused to operate at full stroke capacity for extendedperiods and without any risk whatever of gas locking. The refrigerativevalue lost by the nitrogen in cooling the liquid oxygen is largelyrecovered in the evaporation of the oxygen in interchanger i0. The heatabsorbed by the nitrogen from the pump. which is due mainly to packingfriction, causes a small loss of refrigerating eiect which may becompensated by a. correspondingly slight increase in air feed pressure.

Figures 3 and 4 are modiiications of the form of invention shown inFigure 1 and Figures 5 and 6 are modifications of the form of inventionin Figure 2, which include, among other features, provision forwithdrawing the product oxygen in vapor form and condensing the samebefore passing it to heat exchanger 45.

The product oxygen condensing feature shown in Figs. 3, 4,.5 and 6 isdesigned to eliminate any danger of oil being carried with the oxygeninto the filled cylinders or into any part of the apparatus in whichdetonative combustion might occur. This feature permits the use of oillubricated primary air compressors and avoids the difficulties attendanton water or soap-water lubrication.

Referring ilrst to Figs. 3 and 4, oxygen is Withdrawn through pipe 22which is connected into the base of the column at the point indicated at5i, above the liquid level of pool i9.

The gaseous pure oxygen flowing through this pipe passes through acondenser 52, in which it is liquefied by heat exchange with the airfeed, down-stream from expansion valve I8. The liqueded oxygen then nowsthrough pipe 53 to interchanger 45. in which it is cooled as above deoof condensing the gaseous oxygen has the maior advantage of preventingthe passage of any combustible impurities into any part oi the systemcontaining compressed oxygen.

In addition to the feature of condensing vaporous oxygen product, Fig. 4includes a modification which in some cases may be very desirable. Inthis iol-m of the invention, instead of using the product nitrogen tosubcool the liquid oxygen product in condenser it and to cool the pumpdi, the ieed air downstream of expansion valve it is utilized for thesepurposes. Referring particularly to the drawing, pipe il conducting thefeed air from coil il immersed in the boiling oxygen at the bottom ofthe column, passes the ieed air through expansion valve it to heatexchanger tk The expanded feed air subcools the liquid oxygen product inconduit d6 and then passes out of heat exchanger t5 through conduit ttto the coil It@ surrounding the pump. The expanded iced air refrigeratesthe pump through the medium of this coil and then passes on throughconduit 2l and conduit Bt through condenser di tc the top of the column.In condenser di, the expanded feed air condenses the vaporous oxygenproduct in the same manner as in the modification of Fig. 3.

In the form shown in Fig. 5, oxygen withdrawal pipe it is connected intothe base oi upper column section td', at a point 5d above the liquidlevel of pool ti. The gas thus withdrawn is reiiquened in condenser diby heat interchange with the stream oi crude oxygen owing through pipedi, the condenser being downstream from expansion valve d2. Thecondensed liquid oxygen same as those oi' Figs. l and 2, re-lspectiveiy, and further description of them would densation of the puregaseous oxygen product is accomplished by heat interchange with thecrude oxygen intermediate product and with the intermediate liquidnitrogen product from the lower section of the double column.

Crude oxygen from the base of the lower section flows through pipe 3|,

Nitrogen from pool 2B iiows through pipe 29, and expansion valve tointerchanger 45, pipe 48 to coil I9 and returns to I claim:

l. In combination with a fractionating column for separating a mixtureof low boiling point gases: a pump adapted to handle liquids and achannel connecting the suction ci said pump with a relatively warm vaporspace in said column; a condenser interposed in said channel and a heatinterchanger interposed in said channel between said condenser and saidpump; means for conducting a relatively cool stream of the mixturethrough said condenser toward said column in heat exchange relation witha stream of vapor passing through said condenser; means i'or consaidcondenser and said pump; ducting a relatively cool stream means for conof the mixture vessel.

3. In combination with a fractionating column for separating a mixtureof low boiling point interchanger interposed in said channel betweensaid condenser and said pump; means for conducting a relatively coolstream of the mixture through said condenser toward said column in heatexchange relation with a stream of vapor passing through said condenser;means for conducting a relatively cold uid from said column through saidinterchanger in heat exchange relation with a liquid stream flowing fromsaid condenser toward said pump, and means for bringlng said relativelycold uid into a further heat exchange relation with the liquid-conveyingend of said pump.

4. In combination with a fractionating column for separating a mixtureof low boiling point gases: a pump adapted to handle liquids and achannel connecting the suction of said pump with a relatively warm vaporspace in said column; a condenser interposed in said channel and a heatinterchanger interposed in said channel between said condenser and saidpump; means for conducting a relatively cool stream of the mixturethrough said condenser toward said column in heat exchange relation witha stream of vapor passing through said condenser, and means forconducting a relatively cool fluid from said column through saidinterchanger in heat exchange relation with a liquid stream flowing fromsaid condenser into said pump,

5. In combination with a fractionating column for separating a mixtureof low boiling point gases: a pump adapted to handle liquids and achannel connecting the suction of said pump with a relatively warmproduct-collecting space insaid column; a heat interchanger 'interposedin said channel; means for directing a stream of a relatively coldproduct from said column through said interchanger in heat exchangerelation with the relatively warm column product flowing through saidchannel toward said bringing said relatively cold product into a furtherheat exchange relation with the liquid-conveying end of said pump.

6. In combination with a fractionating column flor separating a mixtureof low boiling point gases: a pump adapted to handle liquids and achannel connecting the suction of said pump with a relatively warmproduct-collecting space in said column; a heat interchanger interposedin said channel, said interchanger providing separated flow paths forfluids passing therethrough; means for directing a stream of arelatively cold product from said column through said interchanger inheat exchange relation with the relatively warm column product flowingthrough said channel toward said pump, and means for conducting saidcolumn product from said interchanger to a point exterior to saidcolumn.

7. In combination with an air fractionating column wherein oxygen isseparated in liquid form: a pump adapted to the pumping of liquids; achannel connecting the suction of said pump with the liquid oxygencollecting space in said column, and means for bringing theliquid-conveying end of said pump into heat exchange relati'on with aproduct of said column colder than said liquid oxygen.

8. In combination with an apparatus producing liquid oxygen and agaseous, nitrogen-rich product; a liquid-oxygen pump; means for bringinga stream of said liquid oxygen into'heat interchange relation with saidnitrogen-rich product and thereby cooling said oxygen stream; means forproducing a further heat interchange between said nitrogen-rich productand said pump, and means for conveying said cooled oxygen stream to saidpump.

9. In combination with an air fractionating column wherein oxygen isseparated in liquid pump, and means for' form: a pump adapted to thepumping of liquids; a channel connecting the suction of said pump withthe liquid oxygen collecting space in said column, and means forbringing the liquid-conveying end of said pump into heat exchangerelation with a fluid from said column colder than said liquid oxygen.

10. The method which comprises withdrawing a stream of oxygen vapor froman air fractionating operation; eecting a heat interchange between saidoxygen vapor and another product of said fractionating operation whichis colder than said oxygen vapor to condense the same to liquid form,reducing the temperature of said liquid stream below the boiling pointof oxygen at the minimum momentary pressure reached in an ensuingpumping step, and pumping said oxygen stream in substantially liquidform.

11. In a method of producing oxygen and conditioning it for delivery toreceiving means, in which air after compression and cooling is rectifiedat a relatively low temperature and reduced pressure thereby producing acold nitrogen product and a liquid oxygen product having a temperaturecorresponding to its boiling point at said reduced pressure; the set ofsteps comprising subiecting fluid from said oxygen product to heatexchange with a colder uid derived from said rectification and therebyforming a sub-cooled liquid oxygen product; pumping such sub-cooledliquid oxygen product to a desired higher pressure, said sub-coolingreducing the liquid oxygen temperature at least sufliciently to preventthe same from iiashing into vapor during such pumping; and convertingthe liquid oxygen at said higher pressure into a gas by heat exchangewith the compressed air to be liquefied.

l2. The process of separating air into its constituents, oxygen andnitrogen, and conditioning the oxygen for delivery to a receivingsystem, said process comprising compressing and subjecting to arefrigerating eiect air at high pressure, subiecting the air to areduction in pressure and llquefaction into two portions, one rich inoxygen and the other rich in nitrogen, subsequently rectifying saidportions to produce separate fractions, one consisting essentially ofoxygen and the other consisting essentially of nitrogen, withdrawingoxygen from said one fraction in the gaseous phase and subjecting it toa condensing operation by heat exchange with a cold product developedduring the separation process, Withdrawing liquidoxygen from thecondensing operation, sub-cooling the withdrawn liquid oxygen by heatexchange with said other fraction, pumping the liquid oxygen to arelatively high pressure, utilizing the cold of the liquid oxygen athigh pressure to produce said refrigerating effect and therebyvaporizing the oxygen.

13. In a method of producing oxygen and conditioning it for deliveryto'receiving means, in which air after compression and cooling isrectified at a relatively low temperature and reduced pressure therebyproducing a cold nitrogen product and a liquid oxygen product having atemperature corresponding to its boiling point at said reduced pressure;the set of steps comprising' subjecting fluid from said oxygen productto heat interchange with a stream of gaseous nitrogen obtained as one ofthe final products of said rectiiication and thereby forming asub-cooled liquid oxygen product; pumping such sub-cooled liquid oxygenproduct to a desired higher pressure, said sub-cooling reducing theliquid oxygen temperature at least sufficiently to prevent the same fromiiashing into vapor during such pumping; and converting the liquidoxygen at said higher pressure into a gas by heat exchange with the'compressed air to thereby cool the air.

14. The method of transferring the product oxygen from an airfractionating operation into a pressure vessel which comprises:withdrawing a stream of oxygen vapor from said operation; condensingsaid vapor and reducing the temperature of said condensed stream to apoint below the boiling point of oxygen at the minimum momentarypressure reached in an ensuing pumping step; stantially liquid form to apressure materially higher than that at which said vapor was condensed;applying an additional external cooling eiect to that portion of theliquid stream in which said higher pressure is created; heating andthereby gasifying said liquid stream, and charging the resultant gasinto a pressure vessel under the pressure initiated in said pumpingstep.

15. The method which comprises: withdrawing a stream of oxygen vaporfrom an air fractionating operation; condensing said vapor and coolingthe condensed stream to a point below the boiling point of oxygen at theminimum m mentary pressure reached in an ensuing pumping step, andpumping said cooled oxygen stream in substantially liquid form to adesired destination.

16. In a procedure in which a stream of oxygen is Withdrawn from an airfractionating operation, the steps comprising: pumping said withdrawnstream in liquid condition, and cooling said stream in transit to saidpumping step to a temperature below the boiling point of oxygen at theminimum momentary pressure reached in said step, by heat interchangewith a stream of the gaseous nitrogen obtained as one of the finalproducts of said fractionating operation.

17. In a procedure in whiclra stream of oxygen is withdrawn from an airfractionating opera-l tion, the steps comprising: pumping said withdrawnstream in liquid condition, and cooling said stream in transit to saidpumping step to a temperature below the boiling point of oxygen at theminimum momentary pressure reached in said step, rst by heat interchangewith the cooled and expanded air feed entering said fractionatingoperation and thereafter by heat interchange with a stream of thegaseous nitrogen obtained as one of the final products of saidoperation.

18. The methodof transferring liquefied product of a fractionatingoperation, in which operation a mixture of component gases havingboiling points substantially below atmospheric tem-' y perature iscompressed and cooled, the compressed and cooled mixture expanded andthe eiuent of the expansion step subjected to the fractionatingoperation to produce a liquefied higher boiling point fraction and agaseous lower boiling point fraction, comprising withdrawing a stream ofthe liquefied higher boiling point fraction from the fractionatingoperation, subcooling the stream of liquefied higher boiling pointfraction by heat exchange with a relatively colder product from thefractionating operation to reduce the temperature of the higher boilingpoint fraction to a point below the boiling point oi' the higher boilingpoint fraction at the minimum momentary pressure reached in an ensuingpumping step. and pumping the subcooled higher boiling point fraction inliquid phase to a relatively high pressure.,

pumping said oxygen stream in sub-v 19.' I'he method of transferringliquefied product of a fractionating operation, in which operation amixture of component gases having boiling points substantially belowatmospheric temperature is compressed and cooled, the compressed andcooled mixture expanded and the eiiiuent of the expansion step subjectedto the fractionating .operation to produce a liquefied higher boilingpoint fraction and a gaseous lower boiling point fraction, comprisingwithdrawing a stream of the liqueed higher boiling point fraction fromthe fractionating operation, subcooling the stream of liqueed higherboiling point fraction by heat exchange with a relatively colder productfrom the fractionating operation to reduce the temperature of the higherboiling point fraction to a point below the boiling point of the higherboiling point fraction at the minimum momentary pressure reached in anensuing pumping step, pumping the subccoled higher boiling pointfraction in liquid phase to a relatively high pressure and heatexchanging the higher boiling point fraction from the pump with themixture of gases going to the fractionating operation to cool themixture and vaporize the higher boiling point fraction.

20. The method of transferring liqueiied product of a fractionatingoperation, in which operation a mixture of component gases havingboiling points substantially below atmospheric temperature is compressedand cooled, the compressed and cooled mixture expanded and the efiluentof the expansion step subjected to the fractionating operation toproduce a liquefied higher boiling point fraction and a gaseous lowerboiling point fraction, comprising withdrawing a stream of the liquefiedhigher boiling point fraction from the fractionating operation,subcooling the stream of liquefied higher boiling point fraction by heatexchange with a relatively colder product from the fractionatingoperation to reduce the temperature of the higher boiling point fractionto a point below the boiling point of the higher boiling point fractionat the minimum momentary pressure reached in an ensuing pumping step,pumping the subcooled higher boiling point fraction 4in liquid phase toa relatively high pressure, and subjecting the higher boiling pointfraction during the pumping step to heat exchange with a relatively coldproduct of the fractionating operation to prevent vaporization of thehigher boiling point fraction during the pumping step.

CARL R. ANDERSON.

REFERENCES CITED The following references are of record in the file Yofthis patent:

UNITED s'rs'rns PATENTS

